Low-vanadium and high-activity SCR catalyst for low-temperature denitrification: Influence of vanadium precursor and surface vanadium concentration

Nitrogen oxides (NO_x), as the main pollutants of air pollution, cause serious harm to the ecological environment and human health. SCR technology is widely used as the most effective method for treating NO_x. The core of SCR technology is SCR catalyst. The reaction temperature of traditional commercial catalysts is difficult to reach the optimal operating temperature range, so expanding the temperature window of V₂O₅/TiO₂ catalysts to the low-temperature region while reducing vanadium loading is a key issue to be solved. A series of V₂O₅/TiO₂ catalysts with different vanadium precursors and different vanadium loadings were prepared by solid-phase synthesis method. The physicochemical properties of the catalyst were analyzed by X-ray diffraction, X-ray photoelectron spectroscopy, temperature programmed desorption of ammonia and temperature programmed reduction of hydrogen. The denitrification activity of the catalyst was evaluated in a fixed bed reactor. The catalysts prepared with vanadyl oxalate (VOC₂O₄·xH₂O) and vanadyl acetylacetonate (VO(acac)₂) as vanadium precursors with a vanadium loading of 5% exhibited the highest denitrification activity, with a stable NO_x conversion of 100% within the temperature range of 200−350 ℃. Compared with the catalysts prepared with ammonium metavanadate (NH₄VO₃) and vanadyl sulfate (VOSO₄·xH₂O) as the vanadium precursors, the maximum activity temperature of VOC₂O₄-V5Ti and VO(acac)₂-V5Ti shifted towards the low-temperature region by about 150 ℃. Furthermore, the denitrification activity of catalyst with a low vanadium content (1%) prepared using VO(acac)₂ precursor was even higher than that of catalyst with a high vanadium content (6%) prepared using NH₄VO₃ precursor. Using VOC₂O₄ and VO(acac)₂ as vanadium precursors could effectively regulate the active sites and polymeric states on the catalysts, and promote the interaction of V atoms with different valence states to form more reductive V species (V⁴⁺), thus exhibiting excellent SCR reactivity. This study provided an effective method for the preparation of low-vanadium and high-activity denitrification catalysts at low temperatures.